1. Field of the Invention
This invention relates to a system and method for sensing a paper roll, and particularly to a system and method for ultrasonically sensing an amount of paper remaining on a paper roll.
2. Description of Background
Receipt printer paper, such as are commonly found with point of sale devices, usually comes in rolls. Before our invention, it has been difficult to for a printer to estimate the amount of paper remaining on a roll. This is in part due to the various roll sizes and varied diameters of the hollow center carriers on which the rolls are mounted. In other words, even if two rolls have the same overall outside diameter, one may have a hollow center carrier with a greater outer diameter, thereby resulting in less paper on that roll.
Currently, the last few feet of the paper on a roll are marked with colored ink. When the operator of the point of sale device notices the colored ink on the paper receipts being dispensed, they know to replace the paper roll, as it will soon run out. This tends to work satisfactorily for point of sale devices that are operated by a staff person of an establishment. However, for self-service devices that dispense receipts, the user (when seeing the colored ink on their receipt) does not reliably notify (if at all) a staff person that the paper roll needs to be replaced.